1. Field of the Invention
The present invention generally relates to cardiac pacing systems and, in particular, to methods and medical systems including implantable medical devices, for automatic characterization of sensors of such implantable medical devices and automatic evaluation of settings, e.g. pacing settings such as VV-delays, of such devices.
2. Description of the Prior Art
Medical devices are implanted in human bodies for e.g. monitoring physiological conditions or treating diseases. One particular example of implantable medical devices is a cardiac rhythm management device including pacemakers and defibrillators implanted in a patient to treat irregular or other abnormal cardiac rhythms by delivering electrical pulses to the patient's heart. Pacemakers are often used to treat patients with bradyarrythmias, that is, hearts that beat too slow or irregularly. Defibrillators are capable of delivering higher energy electrical stimuli to the heart and are often used to treat patients with tachyarrythmias, that is, hearts that beat too quickly.
Such implantable medical devices comprises a number of sensors which are used to sense different physiological parameters of the patient, and in particular of the patient's heart, in order to deliver an accurate and reliable stimuli of the heart with respect to timing, amplitude etc. For example, sensors for determining an activity level of the patient, e.g. an accelerometer, sensors for determining a breathing rate of the patient are often included in such implantable medical devices. In order to obtain a reliable and correct operation of the implantable device, the characteristics and settings of the sensors must be determined in an accurate way.
Today, the normal procedure for determining the sensor characteristics and/or settings, e.g. of an activity sensor of an implanted medical device, is to start the collection of the sensor data via a programmer. The patient is then asked to lie down during a period of time and to perform a walk during a second period of time. In this way, sensor data is registered at two different activity levels; namely at rest and at normal walking.
However, this mainly manual procedure for sensor characterization is associated with a number of drawbacks. For example, the sensor is characterized over a rather limited patient activity level range which may lead to an impaired function of the device due to a non-complete or limited sensor is characterization. Furthermore, it may be difficult for the operator, e.g. the physician, conducting the patient test session to obtain reliable and reproducible results from the test, for example, due to the fact that the exerted workload during the walking is subjective for the patient and the actual workload is difficult to estimate.
A similar procedure is also conducted when setting up or adjusting pacing settings of an implanted medical device, e.g. setting up or adjusting a V-V timing of a pacemaker after an implantation. In this case, the physician and/or nurse measure the cardiac output and adjusts the V-V timing manually and this is repeated until satisfying results are obtained. This procedure is in some cases also combined with activity level measurements, i.e. the patient is asked to lie down during a period of time and to perform a walk during a second period of time. This manual procedure for setting up or adjusting the pacing settings of an implanted device, such as a pacemaker, may, apart from being time consuming, lead to unreliable results, for example, due to the fact that the cardiac output has to be interpreted and connected to a new V-V delay.
Thus, there is a need of an improved and automatized procedure for characterization of rate-responsive sensors of implantable medical devices, such as pacemakers, and for an improved and automatic procedure for evaluation and optimizing of pacing settings of implantable medical devices, such as pacemakers.
United States Patent Application Publication No. 2004/0220636 discloses a system in which an IMD (Implantable Medical Device) programming device receives hemodynamic data from a hemodynamic measurement device (for example an external device) and programs one or more pacing parameters of the IMD as a function of the received pacing data. The IMD programming device is telemetrically linked to the IMD and may read, write, or store, for example, pacing parameters of the IMD to the IMD and/or to the IMD programming device. The hemodynamic measurement device monitors the patient and generates updated hemodynamic data and the programmer may set or adjust the pacing parameters of the IMD as a function of the updated hemodynamic data. However, this system requires that a physician or nurse conducts the test and instructs the patient, for example, in case of determining sensor characteristics at different activity levels, to lie down and to walk during certain periods of time. Accordingly, the system according to United States Patent Application Publication No. 2004/0220636 does not solve all the problems associated with the prior art procedures.
Hence, there remains a need within the art of an improved and automatized procedure for characterization of rate-responsive sensors of implantable medical devices, such as pacemakers, and for an improved and automatic procedure for evaluation and optimizing of pacing settings of implantable medical devices, such as pacemakers.